Respiratory impedance and bronchodilator responsiveness in healthy children aged 2-13 years

BACKGROUND

The forced oscillation technique (FOT) can be used in children as young as 2 years of age and in those unable to perform routine spirometry. There is limited information on changes in FOT outcomes in healthy children beyond the preschool years and the level of bronchodilator responsiveness (BDR) in healthy children. We aimed to create reference ranges for respiratory impedance outcomes collated from multiple centers. Outcomes included respiratory system resistance (R_rs) and reactance (X_rs), resonant frequency (Fres), frequency dependence of R_rs (Fdep), and the area under the reactance curve (AX). We also aimed to define the physiological effects of bronchodilators in a large population of healthy children using the FOT.

METHODS

Respiratory impedance was measured in 760 healthy children, aged 2–13 years, from Australia and Italy. Stepwise linear regression identified anthropometric predictors of transformed R_rs and X_rs at 6, 8, and 10 Hz, Fres, Fdep, and AX. Bronchodilator response (BDR) was assessed in 508 children after 200 µg of inhaled salbutamol.

RESULTS

Regression analysis showed that R_rs, X_rs, and AX outcomes were dependent on height and sex. The BDR cut‐offs by absolute change in R_rs8, X_rs8, and AX were −2.74 hPa s L⁻¹, 1.93 hPa s L⁻¹, and −33 hPa s L⁻¹, respectively. These corresponded to relative and Z‐score changes of −32%; −1.85 for R_rs8, 65%; 1.95 for X_rs8, and −82%; −2.04 for AX.

CONCLUSIONS

We have established generalizable reference ranges for respiratory impedance and defined cut‐offs for a positive bronchodilator response using the FOT in healthy children. Pediatr Pulmonol. 2013; 48:707–715. © 2012 Wiley Periodicals, Inc.Full article with references: https://onlinelibrary.wiley.com/doi/abs/10.1002/ppul.22699Copyright © 2012 Wiley Periodicals, Inc.